In recent years, CAD/CAM systems have been widely used to design dental prostheses such as inlays and crowns by computers to fabricate them by machining with milling machines. Conventionally, with the emphasis on the aesthetic appearance, ceramic materials are generally used as materials for mill blanks to be machined in these systems. However, since ceramics are very hard and brittle materials, dental prostheses fabricated from ceramic mill blanks have problems such as damage to the opposing teeth and cracking caused by impact of machining or occlusion.
In order to solve these problems, mill blanks made of composite materials containing polymer resins and fillers, being hard but not so hard as to damage the opposing teeth, and having excellent impact resistance have recently been developed and used in clinical practice.
For example, Patent Literature 1 describes a mill blank containing a polymer resin and a filler, for use in fabricating a dental prosthesis. For the filler, a filler obtained by finely grinding a material obtained by the sol-gel method, a commercially available irregular-shaped barium glass filler, a filler obtained by grinding quartz with a mill, and an ultrafine particle inorganic filler (average particle size of 40 nm) are studied.
Patent Literature 2 describes a mill blank containing an acrylic resin polymer and an ultrafine particle inorganic filler having an average particle size of 0.01 to 0.04 μm, for use in fabricating a dental prosthesis.